The present invention relates to fiber optic assemblies and methods of making of the same. More specifically, the invention relates to fiber optic assemblies that are manufactured using a single optical fiber strander.
FIGS. 1 and 2 illustrate prior art fiber optic cables containing multiple tight-buffered optical fibers. FIG. 1 depicts a single layer cable 100 that includes multiple tight-buffered optical fibers 101 stranded around a rigid over-coated glass reinforced plastic (GRP) strength member 102. Strength member 102 serves as an anti-buckling member protecting the tight-buffered optical fibers 101 from buckling loads applied to the cable 100; however, it makes for a relatively large and stiff cable. As depicted, aramid yarns 103 are stranded around tight-buffered optical fibers 101. Aramid yarns 103 act as a binder to hold the lay of the optical fibers 101 before extruding jacket 104 thereover. Additionally, aramid yarns 103 inhibit jacket 104 from sticking to the tight-buffered optical fibers 103, thereby preserving optical performance. Prior art cable 100 also includes a ripcord 105 for removing jacket 104.
Prior art cable 100 generally performs poorly in crush and bend testing due to rigid central member 102. During crush testing, optical fibers 101 can be pressed against rigid central member 102, thereby affecting the optical performance of the same. During bend testing, rigid central member 102 can interfere with the movement of the optical fibers within a bend segment. The tight-buffered fibers at the outer edge of the bend have to travel a longer distance than the fibers on the inner edge of the bend. To compensate for the differential length during bending, the optical fibers are stranded so that they are adjacent to, for example, the outside of the bend radius for a portion of the bend, then move towards the inside of the bend radius for an adjacent portion of the bend. If the bend length is less than the lay length of the optical fibers, the optical fibers may kink causing optical attenuation. For this prior art cable, the fiber optic lay length can effectively limit the minimum bend radius for which acceptable optical performance can be achieved.
FIGS. 2 and 3 respectively depict a prior art dual-layer optical fiber cable 200 and a stranding portion of the manufacturing line therefor. As shown, this prior art cable requires tight-buffered optical fibers 201 stranded in an inner layer and an outer layer, which are separated by a intermediate layer of aramid yarns 203. Prior art cable 200 also includes a ripcord 206 and a jacket 205. As shown in FIG. 3, the inner layer of optical fibers and the outer layer of optical fibers must be stranded by a first optical fiber strander 301A, and a second optical fiber strander 301B. Thus, this dual-layer prior art cable is more complicated to manufacture than prior art cable 100. However, optical fibers 201 of cable 200 have more freedom to move compared with optical fibers 101 of cable 100, thereby enabling a smaller bend radius than cable 100.
Likewise, as depicted in FIG. 3, a first and a second yarn strander 302A, 302B must also be employed during the manufacture of this prior art dual-layer cable 200. A significant amount of set-up time is required for manufacturing cable 200 because four separate stranders are required for making the same.
Specifically, prior art cable 200 requires three tight-buffered optical fibers 201 stranded around a central aramid yarn 202 using first optical fiber strander 301A, thereby forming the inner layer of optical fibers. Next, intermediate layer of aramid yarns 203 is stranded around the inner layer of tight-buffered optical fibers for maintaining the stranding of the same. Intermediate layer of aramid yarns 203 are stranded using first yarn strander 302A. Thereafter, the outer layer of optical fibers 201 is stranded around intermediate layer of aramid yarns 203 using second optical fiber strander 301B. Then an outer layer of aramid yarns 204 is stranded around the outer layer of optical fibers 203 using second yarn strander 302B. Intermediate layer of aramid yarns 203 and outer layer of aramid yarns 204 hold the tight-buffered optical fibers together and maintain the stranded lay of each respective layer. Moreover, intermediate layer of aramid yarns 203 inhibits tight-buffered optical fibers 203 from migrating between layers. In other words, individual optical fibers are generally confined to one layer, which prevents entanglement of optical fibers 201 between layers, which may cause undesirable optical attenuation.
The present invention is directed to a fiber optic cable including at least one central strength member, a first layer of optical fibers, a second layer of optical fibers, and a jacket surrounding the first and second layers of optical fibers. Where the at least one central strength member essentially lacks anti-buckling strength. Additionally, the fiber optic cable excludes a separation layer between the first layer of optical fibers and the second layer of optical fibers.
The present invention is also directed to a fiber optic cable including a central member, a first plurality of S-Z stranded optical fibers, a second plurality of S-Z stranded optical fibers, and a jacket disposed about the second plurality of S-Z stranded optical fibers. The first and second layers of S-Z stranded optical fiber being disposed in respective radial locations and having lay lengths that are the same. Additionally, the first plurality of S-Z stranded optical fibers are in phase with the second plurality of S-Z stranded optical fibers along the length of the cable because they are both stranded by a common strander.
The present invention is further directed to a fiber optic assembly including a plurality of optical fibers, and a binder layer. The plurality of optical fibers being stranded around in at least two radially distinct adjoining layers. The optical fibers in the adjoining layers having the same lay length and are in phase so that the optical fibers are free to radially migrate between adjoining layers in response to external forces.
Additionally, the present invention is directed to a method of manufacturing an optical fiber assembly including the steps of paying off a plurality of optical fibers, stranding the plurality of optical fibers in a single stranding process, placing a binder layer about the second layer of optical fibers. The plurality of optical fibers forming a first layer and second adjoining layers.